What is the difference between HashMap, TreeMap, and LinkedHashMap?

Difficulty: 5/10

ordering, performance, null handling

HashMap vs TreeMap vs LinkedHashMap

In Java, HashMap, TreeMap, and LinkedHashMap provide different ordering and performance characteristics. HashMap is optimized for general key-value lookup, TreeMap maintains keys in sorted order using a tree, and LinkedHashMap maintains a predictable iteration order using a linked ordering structure in addition to hashing.

javascript

1
HashMap: expected O(1) get/put; no general sorted iteration guarantee.
2
LinkedHashMap: expected O(1) get/put; maintains insertion order, and can also be configured for access order.
3
TreeMap: O(log n) get/put/remove; maintains keys in sorted order.
4
HashMap is usually preferred for pure key-based lookup.
5
TreeMap is appropriate for range queries, sorted traversal, and predecessor/successor operations.
6
LinkedHashMap is useful when deterministic iteration order is required.

Scenario Questions

0-2 years experience

2-5 years experience

1We have a feature that caches recent search queries and needs to evict the oldest entry when the cache exceeds 1000 items. Which map would you use and how would you implement the eviction?

Follow-up Questions